The "third-party ownership" of footballers was banned by the Premier League after the "economic rights" of the Argentinian stars Carlos Tevez and Javier Mascherano were discovered to still be owned by two offshore companies when they signed for West Ham United in 2006. The Premier League's chief executive, Richard Scudamore, has compared to "indentured slavery" this practice, by which investors, often operating anonymously via tax havens, buy stakes in players and receive a share of the transfer fee when they are sold.

The revelation that players' "economic rights" could be "owned" by investors, and the money for their signing not be paid wholly to the selling club, shocked English football, but it is common in eastern Europe, Portugal and Spain, and widespread in South America, notably Brazil. A report in August by the consultants KPMG found that 27%-36% of the players in Portugal's Primeira Liga are owned by third-party investors, and the practice has "greatly increased" in Spain, particularly at financially struggling clubs. Such clubs argue that selling a share in a player to investors brings money up front and enables them to keep the player for longer, before sharing the proceeds with the investors when the player leaves.

West Ham were ultimately fined £5.5m for not disclosing all the documents relating to the Tevez and Mascherano signings, and a series of court cases followed, before the Premier League clubs agreed to prohibit third-party ownership of their own players.

In December, Platini said: "We cannot accept that players are owned by an agent or an entity, or financial institutions. It is hard to understand that footballers, who have battled so much to be independent of clubs, ending the old contract situation [with the 1995 Bosman ruling], are now controlled by third-party funds. I do not accept that. I am going to fight with all my strength against that."

Fifa's rules prohibit "third-party influence" on clubs' employment and transfers, but still allow third-party investment. The two studies commissioned by Fifa are seeking all the facts about the practice, "integrity considerations", and the different regulations worldwide, before considering what to do.

Uefa says European football transfers amounted to €3bn last summer, and of that, fully 30%, €900m, was paid to agents. Gianni Infantino, Uefa's general secretary, said that did not include more money going out to third parties, which he argues is a short-term, destructive fix to clubs' financial difficulties. Infantino pledged to "fight alone" and ban the practice in Europe if Fifa are too slow.

"This situation cannot continue," he said. "What matters is that clubs have a stable future. Uefa takes issue with all investment funds related to third-party ownership of players, [where] for instance, 30% of the transfer fee goes to the agents. That's great for them, because they have worked well. But we have to have financial transparency, it must be clear where the money is going. It is a matter of integrity.

"There are players and managers that belong to an investment fund and are at different clubs, clubs that are competing against each other. That endangers the integrity of football. Obviously everyone wants to earn money, but we have to protect the integrity of our game."